Potassium sulfate is neutral in the soil. Potassium nitrate will raise pH slightly, however, I have not had a problem using it as the potassium source combined with ammonium sulfate. Ammonium sulfate will acidify many soils if used as the nitrogen source. The reason why prefer potassium nitrate is its high solubility and total absence of chlorine. My soils usually have too much to begin with. Why would I want to add more with every routine fertilization?